NHibernate 3.0: TransactionScope and Auto-Flushing

Question

In NHibernate 3.0, FlushMode.Auto does not work when running under an ambient transaction only (that is, without starting an NHibernate transaction). Should it?

using (TransactionScope scope = new TransactionScope()) 
{
    ISession session = sessionFactory.OpenSession();
    MappedEntity entity = new MappedEntity() { Name = "Entity", Value = 20 };
    session.Save(entity);

    entity.Value = 30;
    session.SaveOrUpdate(entity);

    // This returns one entity, when it should return none
    var list = session.
               CreateQuery("from MappedEntity where Value = 20").
               List<MappedEntity>();
}

(Example shamelessly stolen from this related question)

In the NHibernate source I can see that's it's checking whether there's a transaction in progress (in SessionImpl.AutoFlushIfRequired), but the relevant method ( SessionImpl.TransactionInProgress) does not consider ambient transactions - unlike its cousin ConnectionManager.IsInActiveTransaction, which does consider ambient transactions.

Answer 1

Good news. Thanks to Jeff Sternal (who nicely identified the problem) I updated https://nhibernate.jira.com/browse/NH-3583 and thanks to the NH staff, there's already a fix and a pull request so in the upcoming release 4.1.x.x this ISSUE will be fixed.

Answer 2

You should use an explicit NHibernate transaction always.

using (TransactionScope scope = new TransactionScope()) 
using (ISession session = sessionFactory.OpenSession())
using (ITransaction transaction = session.BeginTransaction())
{
    //Do work here
    transaction.Commit();
    scope.Complete();
}

I see you also wrote in the NH dev list - while this can change in the future, that's how it works now.

Answer 3

The answer provided by Diego does not work in the case where you have an oracle database. (releated question). The session.BeginTransaction will fail because the connection is already part of a transaction.

Looks like we have to write some code around this problem in our application (WCF,NHibernate, Oracle), but it just feels like something that NHibernate should provide out of the box. So if anyone has a good answer, it would be really appreciated.

Answer 4

For me, I don't know the reason behind, but by forcing session flush before session is disposed seemed to worked for me. e.g. using(session) { //do your work

session.Flush(); }

I verified that this works with my distributed transaction, since without doing this, I always get "transaction has aborted" when TransactionScope is disposed.

Even set session.FlushMode to Commit did NOT work for me.